Relevamiento de los principales grupos de vertebrados e invertebrados del estuario externo del río Negro, Argentina

Abstract

Estuaries are highly dynamic and complex environments that provide significant economic, socio-cultural, and ecological benefits. Their dynamics are strongly influenced by tidal regimes, continental drainage, and atmospheric forces. The Negro River estuary is a unique ecosystem shared between the provinces of Río Negro and Buenos Aires, Argentina. It is the most significant allochthonous watercourse in the country and the second largest in the region in terms of water volume. Despite its notable biodiversity and its role as a key biogeographical transition zone, comprehensive faunal studies in the area remain scarce. In this context, the main objective of this study was to conduct a seasonal survey and inventory of the fauna associated with the outer estuary (marine mammals, reptiles, birds, fish, and macroinvertebrates) to provide essential tools for resource management. Seasonal sampling was carried out between November 2021 and October 2022 on both banks. Physicochemical parameters—including temperature, pH, salinity, conductivity, and dissolved oxygen—were recorded to characterize the area. Fauna presence was identified using various techniques, such as netting, direct observation, and transects. Taxonomically, 56 species of vertebrates and invertebrates were identified during field surveys. This information was integrated with bibliographic data and citizen science reports, resulting in a comprehensive inventory of 98 species (distributed across 79 families and 53 orders). The presence of key conservation species listed as "Vulnerable" by the IUCN was confirmed, including the Franciscana dolphin (Pontoporia blainvillei), the Bottlenose dolphin (Tursiops truncatus), and the Patagonian seahorse (Hippocampus patagonicus). Additionally, five exotic species were recorded, highlighting the first record of the European green crab (Carcinus maenas) in the area. Physicochemical analysis revealed marked temporal variation driven by the interaction between river discharge and marine influence, with lower salinity levels recorded during autumn and winter. Biodiversity indices showed lower fish diversity in summer (Simpson Index, D=0.45), while the Jaccard Index for birds (0.47) indicated significant differences in composition between both riverbanks. This work represents the first comprehensive faunal survey of the area, underscoring its ecological importance as a breeding and feeding ground. Furthermore, it highlights current threats—such as invasive species and anthropic pressures—and reinforces the urgent need to declare the estuary a Protected Natural Area through coordinated interprovincial management.